1. Field of the Invention
The present invention relates to devices for sealing cavities in airframes through which control surfaces are deployed and for reducing aerodynamic drag effects by reducing airframe discontinuities after the control surfaces are deployed.
2. Background of the Invention
Missiles, projectiles and other airframes that use deployable fins, wings, strakes, canards and other deployable flight control surfaces have increased aerodynamic drag in the deployed state as compared with airframes that use fixed control elements. Current deployment methods and apparatus generally do not include techniques for reducing the drag after the control surfaces are released in order to minimize the mechanical complexity thereby improving the reliability of the system.
Three constructions which have been used with some success to reduce drag while maintaining the body cross-sectional area essentially constant when the surfaces are in the retracted state, are
1. Folding of surface into the main airframe body through slots in the airframe skin,
2. Folding of surface into flattened areas on the outside of the main airframe body, and
3. Wrapping of surfaces around the airframe body in shaped reliefs.
FIGS. 1A-1D illustrate a prior art design where a deployable body is folded into a slot. As depicted, deployable surfaces (a) are housed prior to deployment in slot (d) cut into the body of the airframe (b) defined by external skin (c). Hinge cutouts (e) may be used to provide room for hinge (f) after the deployable surface (a) is released. Slots (d) usually remain open after deployment (see FIG. 1D) thereby constituting a source of aerodynamic drag that affects the flight characteristics of airframe (b).
FIGS. 2A-2C illustrate another prior art design where a deployable aerodynamic surface is folded into flattened areas on the outside skin. In this design, recesses or flats (h) are provided such that the deployable surface (a) is within the projected cross section of the airframe when in the non-deployed state (FIG. 2B). When the fins or other deployable control surfaces (a) are deployed, flats (h) remain open thereby disrupting the airflow as it passes over the airframe skin (c).
FIGS. 3A-3C illustrate a third construction characteristic of the prior art for deployable control surfaces using wraparound fins or surfaces. As seen best in FIGS. 3B and 3C, aerodynamic surfaces (a) unwrap leaving recesses (i) on the airframe (b) thereby disrupting airflow.
All of the above-described constructions fail to provide a continuous smooth airframe after the aerodynamic surfaces are deployed. These airframe discontinuities disrupt the airflow thereby inducing turbulence and increasing drag. The turbulent airflow in the vicinity of the control surfaces can further reduce control system effectiveness.
Other prior art constructions have attempted to use movable panels to close the slots or other openings after deployment of the fins or other control surfaces. U.S. Pat. No. 4,007,896 to Reynolds and U.S. Pat. No. 4,640,477 to Pace are representative in that both use closure panels which are hinged at one end to the airframe body and utilize springs to move the panels to a sealing position following deployment. However, these constructions have not been entirely successful due to the added complexity caused by the separate spring element and the inability to consistently provide adequate sealing engagement between the non-hinged panel end and the airplane skin.